1. Field of the Invention
The present invention relates to a method of production of a multilayer ceramic capacitor or other multilayer ceramic electronic device.
2. Description of the Related Art
In recent years, as the material for internal electrode layers used in a multilayer ceramic capacitor, a typical example of a multilayer ceramic electronic device, it has become possible to use nickel and other inexpensive base metals instead of platinum, palladium, and other expensive precious metals. Major reductions in cost have been realized.
However, for suitable metallization of internal electrode layers using base metals, the green chip has to be fired in a reducing atmosphere. To give the dielectric materials resistance to reduction in firing in a reducing atmosphere, sometimes Mn is added to the dielectric layers contained in the green chips. Further, to enable reoxidation of the dielectric layers in the sintered body after firing in a reducing atmosphere, the sintered body is sometimes annealed.
In the past, when adding Mn to the dielectric layers, the sintered body obtained by firing a green chip containing the dielectric layers had to be suitably annealed or else MnO would segregate (precipitate) in the vicinity or at the ends of the internal electrode layers—resulting in problems such as structural defects or disconnects of internal electrode layers. That is, if annealing was not suitably performed, it became a cause of a drop in the yield, reliability, etc. of the capacitors.
In the past, after firing the green chip, the practice had been to anneal the obtained sintered body just once at a holding temperature of for example about 1000 to 1200° C. (see Patent Publication 1: Japanese Patent Publication (A) No. 2002-80279 and Patent Publication 2: Japanese Patent Publication (A) No. H08-8137).
However, with a single annealing, if the holding temperature is too low, there is a tendency for the reoxidation of the dielectric layers to become insufficient, the insulation resistance to deteriorate, and the accelerated life (highly accelerated life test value) to also become shorter. Conversely, if the holding temperature is too high, the reoxidation of the dielectric layers is performed well, but even the internal electrode layers end up being oxidized and therefore not only does the capacity fall, but also there is tendency for the dielectric base material to end up being reacted with and the capacity-temperature characteristic, insulation resistance, and accelerated life to deteriorate.
That is, with just a single annealing, optimization of the stabilization (holding) temperature and time was difficult.